[PATCH v6 3/5] Implement modalias sysfs attribute for modules

Allen Webb
2022-12-02T22:48:15Z

When the modalias attribute is read, invoke a subsystem-specific
callback for each driver registered by the specific module.

The intent of the new modalias attribute is to expose the
match-id-based modaliases to userspace for builtin and loaded kernel
modules.

Signed-off-by: Allen Webb <allenwebb@google.com>
---
include/linux/device/bus.h | 7 +++++
kernel/module/sysfs.c | 57 +++++++++++++++++++++++++++++++++++++-
2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index 82a5583437099..cce0bedec63d9 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -61,6 +61,10 @@ struct fwnode_handle;
* this bus.
* @dma_cleanup: Called to cleanup DMA configuration on a device on
* this bus.
+ * @drv_to_modalias: Called to convert the matching IDs in a
+ * struct device_driver to their corresponding modaliases.
+ * Note that the struct device_driver is expected to belong
+ * to this bus.
* @pm: Power management operations of this bus, callback the specific
* device driver's pm-ops.
* @iommu_ops: IOMMU specific operations for this bus, used to attach IOMMU
@@ -107,6 +111,9 @@ struct bus_type {
int (*dma_configure)(struct device *dev);
void (*dma_cleanup)(struct device *dev);

+ ssize_t (*drv_to_modalias)(struct device_driver *drv, char *buf,
+ size_t count);
+
const struct dev_pm_ops *pm;

const struct iommu_ops *iommu_ops;
diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
index 8dafec7455fbe..651c677c4ab96 100644
--- a/kernel/module/sysfs.c
+++ b/kernel/module/sysfs.c
@@ -5,6 +5,8 @@
* Copyright (C) 2008 Rusty Russell
*/

+#include <linux/device/bus.h>
+#include <linux/device/driver.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
@@ -240,11 +242,64 @@ static inline void add_notes_attrs(struct module *mod, const struct load_info *i
static inline void remove_notes_attrs(struct module *mod) { }
#endif /* CONFIG_KALLSYMS */

+/* Track of the buffer and module identity in callbacks when walking the list of
+ * drivers for each bus.
+ */
+struct modalias_bus_print_state {
+ struct module_kobject *mk;
+ char *buf;
+ size_t count;
+ ssize_t len;
+};
+
+static int print_modalias_for_drv(struct device_driver *drv, void *p)
+{
+ struct modalias_bus_print_state *s = p;
+ struct module_kobject *mk = s->mk;
+ ssize_t len;
+ /* Skip drivers that do not match this module. */
+ if (mk->mod) {
+ if (mk->mod != drv->owner)
+ return 0;
+ } else if (!mk->kobj.name || !drv->mod_name ||
+ strcmp(mk->kobj.name, drv->mod_name))
+ return 0;
+
+ if (drv->bus && drv->bus->drv_to_modalias) {
+ len = drv->bus->drv_to_modalias(drv, s->buf + s->len,
+ s->count - s->len);
+ if (len < 0)
+ return len;
+ s->len += len;
+ }
+ return 0;
+}
+
+static int print_modalias_for_bus(struct bus_type *type, void *p)
+{
+ return bus_for_each_drv(type, NULL, p, print_modalias_for_drv);
+}
+
static ssize_t module_modalias_read(struct file *filp, struct kobject *kobj,
struct bin_attribute *bin_attr,
char *buf, loff_t pos, size_t count)
{
- return 0;
+ struct module_kobject *mk = container_of(kobj, struct module_kobject,
+ kobj);
+ struct modalias_bus_print_state state = {mk, buf, count, 0};
+ int error = 0;
+
+ if (pos != 0)
+ return -EINVAL;
+
+ error = bus_for_each(&state, print_modalias_for_bus);
+ if (error)
+ return error;
+
+ /*
+ * The caller checked the pos and count against our size.
+ */
+ return state.len;
}

/* Used in kernel/params.c for builtin modules.
--
2.37.3